The present invention relates to a balancer system for use in an internal combustion engine such as a motorcycle engine or the like.
Some reciprocating internal combustion engines for use on motorcycles incorporate a balancer system to reduce vibrations during the engine operation. Such a balancer system typically comprises a primary counterbalance for reducing primary vibrations, the primary counterbalance being rotatable about an axis parallel to the crankshaft at the same speed as the crankshaft in the opposite direction to the crankshaft, and, if necessary, a secondary counterbalance for reducing secondary vibrations, the secondary counterbalance being rotatable about an axis parallel to the crankshaft at a speed twice that of the crankshaft.
One balancer system which has a pair of primary counterbalances is disclosed in Japanese Laid-Open Utility Model Publication No. 55(1980)-142733. Another balancer system with an additional pair of secondary counterbalances is disclosed in Japanese Laid-Open Utility Model Publication No. 58(1983)-20750.
In the disclosed systems, the primary and secondary counterbalances are supported on respective dedicated balancer shafts which extend parallel to the crankshaft, and rotated about and in unison with the balancer shafts in ganged relation to the crankshaft.
If the centers of gravity of the primary or secondary counterbalances were axially spaced from the axial center of the crankshaft where it is connected to the piston, then a couple of forces would be produced in directions normal to the balancer shaft during rotation of the primary or secondary counterbalances. To avoid the generation of such a couple of forces, the primary or secondary counterbalances are mounted on the balancer shaft at its axial center.
Usually, the counterbalances are supported on the respective balancer shafts in the conventional balancer systems. If there are employed both a pair of primary counterbalances and a pair of secondary counterbalances, therefore, the number of components of the balancer system is large, and the internal combustion engine which incorporates the balancer system is relatively heavy and large in size.
With the primary and secondary counterbalances mounted on the respective balancer shafts, complex mechanisms are required to operatively couple the balancer shafts to the crankshaft for ganged rotation. Use of such complex mechanisms also adds to the number of parts of the balancer system.
Since the counterbalances are mounted on the balancer shafts at their axial centers, it is difficult to install other components such as gears on the axially central regions of the balancer shafts. The balancer shafts are dedicated to the support of the counterbalances, and hence cannot effectively utilized for other purposes. Accordingly, the prior balancer shaft arrangement has presented an obstacle to efforts to reduce the number of parts, weight, and size of the balancer system and hence the engine.